Hydraulic control circuit for a priority and for a secondary hydraulic consumer

ABSTRACT

The invention concerns a hydraulic control circuit in which the pressure medium conveyed by a hydraulic pump of variable delivery ( 10 ) is fed, in each case via a metering aperture ( 17, 31 ), as a priority to a first hydraulic consumer ( 14 ) and only secondly to a second hydraulic consumer ( 15 ). A priority control system is now produced without additional delivery losses and with sufficient amounts of pressure medium being conveyed in that the valve member ( 48 ) of the priority valve ( 45 ) can be acted upon in the closure direction of the connection between the first connection ( 46 ) and the second connection ( 47 ) by a pressure prevailing in a line section ( 13 ) upstream of the first metering aperture ( 17 ).

FIELD AND BACKGROUND OF THE INVENTION

The invention concerns from a hydraulic control circuit, by means ofwhich a primary first hydraulic consumer and a secondary secondhydraulic consumer can be supplied with pressure medium in general 1.

Such a hydraulic control circuit is known from DE 43 28 283 A1. In this,the pressure medium flows to the two hydraulic consumers in each casevia a metering diaphragm, the first metering diaphragm assigned to theprimary first hydraulic consumer being preceded by a pressurecompensator, and the second metering diaphragm assigned to the secondarysecond hydraulic consumer being followed by a pressure compensator. Withthe aid of the pressure compensators, if a sufficient quantity ofpressure medium is delivered, constant pressure differences aremaintained via the metering diaphragms, irrespective of the loadpressures of the hydraulic consumers, so that the pressure mediumquantity flowing to a hydraulic consumer depends only on the openingcross section of the respective metering diaphragm. An adjustablehydraulic pump usually serves as a pressure medium source and is capableof being controlled as a function of the highest load pressure in such away that the pressure in an inflow line is above the highest loadpressure by the amount of a specific pressure difference. The pressurecompensator following the second metering diaphragm is acted upon in theopening direction by the pressure downstream of the second meteringdiaphragm and in the closing direction by a control pressure whichprevails in a rear control space and which usually corresponds to thehighest load pressure of all the hydraulic consumers supplied by thesame hydraulic pump. If a plurality of hydraulic consumers, to whichpressure medium flows in each case via a metering diaphragm and apressure compensator which follows the latter and which is acted upon atthe rear by the highest load pressure, are actuated simultaneously, thepressure medium quantities flowing to them are reduced in equal ratio ifthe pressure medium quantity delivered by the hydraulic pump is lowerthan the pressure medium part quantities required. A control withload-independent throughflow distribution (LUDV control) is referred toin this case. Hydraulic consumers controlled in this way are called, inbrief, LUDV consumers. Since, in an LUDV control, the highest loadpressure is also sensed and an inflow pressure lying above the highestload pressure by the amount of a specific Δp is generated by thepressure medium source, an LUDV control is a special instance of aload-sensing control (LS control).

There is no load-independent throughflow distribution in the case of aplurality of hydraulic consumers, to which pressure medium flows in eachcase via a metering diaphragm with a preceding pressure compensatorwhich is acted upon in the closing direction only by the pressureupstream of the metering diaphragm and in the opening direction only bythe load pressure of the respective hydraulic consumer and by acompression spring. Only an LS control and an LS consumer are available.DE 43 28 283 A1, then, discloses priority switching between an LSconsumer and one or more LUDV consumers, in which the LS consumer issupplied as primary consumer with pressure medium. For this purpose, apriority valve is provided, which has a first connection, connected to aline section upstream of the first metering diaphragm, and a secondconnection, connected to the load signaling line, and the valve memberof which is capable of being acted upon, in the direction of the openingof the connection between the first connection and the secondconnection, by the load pressure of the primary hydraulic consumer, thatis to say of the LS consumer, and by an additional force. The priorityvalve in the control according to DE 43 28 283 A1 is acted upon, in thedirection of the closing of the connection between the first connectionand the second connection, by the pressure in the second connection.Although this ensures that the LS consumer is supplied as primaryconsumer with pressure medium, the pressure in the inflow line isunnecessarily high in specific situations, so that power losses occur.Such a situation arises, for example, when the load pressure of theprimary hydraulic consumer is higher than the load pressure of thesecondary hydraulic consumer. A pressure lying above the load pressureof the primary hydraulic consumer by the amount of a pressure differenceequivalent to the additional force acting on the valve member of thepriority valve is then built up in the load signaling line. Theregulation of the hydraulic pump, in turn, gives rise, in the inflowline, to a pressure lying above the pressure in the load signaling lineby the amount of a specific Δp, so that the pressure in the inflow linelies above the load pressure of the primary hydraulic consumer by anamount more than the regulating Δp at the regulating member of thehydraulic pump.

While a priority control between an LS consumer and an LUDV consumer isdisclosable by DE 43 28 283 A1, DE 35 07 122 C2 shows a priority controlbetween two LS consumers. A pressure medium quantity thus flows to thesetwo hydraulic consumers in each case via a metering diaphragm and apressure compensator which precedes this metering diaphragm and which isacted upon in the closing direction by the pressure upstream of themetering diaphragm. The pressure compensator which is assigned to theprimary hydraulic consumer is acted upon in the opening direction by theload pressure of this hydraulic consumer and by a compression spring.The pressure compensator for the secondary hydraulic consumer is actedupon in the closing direction likewise by a compression spring and,moreover, by a pressure picked off between a fixed throttle and aproportional diaphragm which serves as a priority valve and which isconnected between the fixed throttle and a tank line and is controlledby the pressure difference at the metering diaphragm of the primaryhydraulic consumer. In the event of undersaturation, that is to say whenan insufficient quantity of pressure medium is conveyed, the pressuredifference at the metering diaphragm of the hydraulic consumer to besupplied as primary consumer with pressure medium decreases, so that theproportional diaphragm opens somewhat, the pressure between the latterand the fixed throttle falls somewhat and the pressure compensator ofthe hydraulic consumer to be supplied as secondary consumer withpressure medium closes until sufficient pressure medium is availableagain for the primary hydraulic consumer.

SUMMARY OF THE INVENTION

The object of the invention is to develop further a hydraulic controlcircuit by means of which an LS consumer is to be supplied with pressuremedium as primary consumer with respect to one or more LUDV consumers,in such a way that excessive power losses are avoided during operation.

According to the invention, the valve member of the priority valve canbe acted upon, in the direction of the closing of the connection betweenthe first connection and the second connection, by a pressure prevailingin a line section upstream of the first metering diaphragm. In thissurprisingly simple solution to the problem, when the load pressure ofthe LS consumer is higher than the load pressure of a parallel-actuatedLUDV consumer, the load signaling line is acted upon by the loadpressure of the LS consumer, not by a higher pressure. Consequently, inthe inflow line too, only a pressure which lies above the load pressureof the LS consumer by the amount of the regulating Δp at the hydraulicpump is built up. If the load pressure of the LS consumer is lower thanthe load pressure of a parallel-actuated LUDV consumer, the loadpressure of the LUDV consumer or the highest load pressure of aplurality of simultaneously actuated LUDV consumers prevails in the loadsignaling line.

Advantageous refinements of a hydraulic control circuit.

A feature of the invention, the additional force acting on the valvemember of the priority valve in the direction of the opening of theconnection between the first connection and the second connection isadvantageously generated by a spring.

For a regulation which is not susceptible to vibration, it seemsfavorable if the priority valve is formed as a proportional valve.

The pressure difference at the first metering diaphragm is sensed by thepriority valve. Since, in the event of undersaturation, the pressurecompensator preceding the first metering diaphragm is fully open, acontrol space on the valve member of the priority valve can be connectedto the inflow line upstream of the first pressure compensator. This maybe advantageous in terms of the design of the individual components ofthe control. It may also be advantageous, wherein a control pressurespace on the valve member of the priority valve and the first connectionof the priority valve are connected to the inflow to the first meteringdiaphragm on the same side of the first pressure compensator.

According to a further feature of the invention, there is providedaround the priority valve a bypass line which connects a flow pointdownstream of the first metering diaphragm to the load signaling lineand in which is arranged a nonreturn valve opening toward the loadsignaling line. What is achieved in this way is that, insofar as the LSconsumer is load-carrying, that is to say has the highest load pressure,this load pressure prevails in the load signaling line and, if there isa sufficient quantity of pressure medium for all the consumers actuated,the pressure difference is determined via the first metering diaphragmby the preceding pressure compensator. Only in the event ofundersaturation is the pressure difference determined by the additionalforce at the priority valve, to which a lower pressure difference thanthe spring force at the first pressure compensator is normallyequivalent. Another feature of the invention prevents pressure mediumfrom flowing out of the load signaling line into the inflow line whenthere is still no pressure built up by the hydraulic pump.

BRIEF DESCRIPTION OF THE DRAWINGS

Several exemplary embodiments of a hydraulic control circuit accordingto the invention are illustrated in the drawings. The invention isexplained in more detail with reference to the figures of these drawingsin which

FIG. 1 shows a first exemplary embodiment, in which the first connectionand a control space of the priority valve are jointly connected to theinflow upstream of the pressure compensator assigned to the primaryhydraulic consumer,

FIG. 2 shows a second exemplary embodiment, in which the firstconnection and a control space of the priority valve are connected tothe inflow downstream of the pressure compensator,

FIG. 3 shows a third exemplary embodiment, which has a bypass linearound the priority valve, and

FIG. 4 shows the circuit diagram of a variable displacement pump,including regulating valves, such as is capable of being used in theexemplary embodiments according to FIGS. 1 to 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to FIG. 1, a variable displacement pump 10 with an adjustmentmeans 11 sucks in pressure medium from a tank 12 and discharges it intoa system of inflow lines 13. A first hydraulic consumer 14, which isformed as a synchronous cylinder, and at least one second hydraulicconsumer 15, which is a differential cylinder, are supplied withpressure medium via the inflow lines. The direction and speed of thesynchronous cylinder 14 are determined by appropriate actuation of a 4/3proportional directional valve 16, the valve slide of which isspring-centered in a middle position, in which the four workingconnections and a control connection 18 of the directional valve 16 areblocked. When the valve slide is displaced out of its middle position inone direction or the other, a metering diaphragm (device) 17 is openedto a varying extent, depending on the distance over which the valveslide is moved. The control connection 18 is connected, downstream ofthe metering diaphragm, to the forward flow to the synchronous cylinder14.

Inserted between the system of inflow lines 13 and an inflow connection19 of the directional valve 16 is a 2-way pressure compensator 20, theregulating piston of which is acted upon in the direction of the closingby the pressure upstream of a metering diaphragm 17 and in the directionof the opening, via a control line 61, by the pressure in the controlconnection 18 of the directional valve 16, that is to say by the loadpressure of the synchronous cylinder 14, and by a regulating spring 21.The force of the regulating spring 21 is such that a pressure differenceof, for example, 15 bar across a metering diaphragm 17 is equivalent toit.

Thus, while the first pressure compensator 20 assigned to the firsthydraulic consumer 14 precedes the first metering diaphragm 17, thesecond pressure compensator 30 assigned to the second hydraulic consumer15 follows a second metering diaphragm (device) 31. For the directionalcontrol of the differential cylinder 15, there is arranged between thesecond pressure compensator 30 and the differential cylinder adirectional valve 32, via which, as compared with the pressure drop atthe metering diaphragm 31, an appreciable pressure drop no longer occurswhen the differential cylinder 15 is actuated. The metering diaphragm 31and the control grooves necessary for the directional control are formedin a known way on the same valve slide, so that directional control andspeed control in each case readily take place jointly. The regulatingpiston 33 of the pressure compensator 30 is acted upon at the front, inthe direction of the opening of the connection between the meteringdiaphragm 31 and the directional valve 32, by the pressure downstream ofthe metering diaphragm and at the rear, in the direction of the closingof the connection, by a control pressure prevailing in a controlpressure space 34 and by a weak compression spring 35, to which apressure of, for example, only 0.5 bar is equivalent. The front side ofthe regulating piston 33 is connected to the control pressure space 34via a duct 36 running in the regulating piston, there being arranged inthe duct 36 a nonreturn valve 37 opening toward the control pressurespace.

Further metering diaphragms, pressure compensators and directionalvalves for further hydraulic consumers may be connected to the system ofinflow lines 13 in parallel with the metering diaphragm 31, the pressurecompensator 30 and the directional valve 32 for the second hydraulicconsumer 15. In this case, the control pressure spaces 34 of all thepressure compensators 30 are connected to one another, so that the samepressure prevails in these control pressure spaces. When a secondhydraulic consumer is actuated, the regulating piston 33 of the pressurecompensators seek to assume a position in which a pressure establishedon their front side is higher than that in the control pressure spaces34 only by the amount of the pressure difference equivalent to the forceof the compression spring 35.

Even if the first hydraulic consumer 14 is ignored completely, thehighest load pressure of all the actuated second hydraulic consumers 15is in each case introduced into the control pressure spaces 34 via theducts 36 and the nonreturn valves 37.

The control pressure spaces 34 are connected to a load signaling line 38which leads to the adjustment means 11 of the pump 10. In particular, asis apparent from FIG. 4, the load signaling line 38 leads to aregulating valve 39 having three connections, one of which is connectedto an actuating cylinder 40 of the variable displacement pump 10. Afurther connection of the regulating valve 39 is connected to an inflowline 13 and the third connection to the tank 12. The regulating pistonof the regulating valve 39 is acted upon, in the direction of connectingthe first connection to the second connection, by the pressure in theinflow line 13 and, in the direction of connecting the first connectionto the third connection, by the pressure in the load signaling line 38and by a regulating spring 41. Variable displacement pumps andregulating valves according to the circuit diagram shown in FIG. 4 aregenerally known and are readily obtainable on the market. There istherefore no need to discuss them in any more detail. It may be pointedout merely that the pump regulation causes a pressure to be establishedin the inflow line 13 which lies above the pressure in the loadsignaling line 38 by the amount of a pressure difference equivalent tothe force of the regulating spring 41. The pressure difference is, forexample, 20 bar, that is to say is higher than the pressure differenceof 15 bar equivalent to the force of the regulating spring 21 of thefirst pressure compensator 20.

The first hydraulic consumer 14 is to be supplied with pressure mediumas primary consumer before the second hydraulic consumer 15. For thispurpose, a priority valve 45 is provided, which is formed as aproportional diaphragm with an inlet 46 and an outlet 47. The latter isconnected to the load signaling line 38. The inlet 46 is connected,upstream of the pressure compensator 20, to an inflow line 13. The valvemember 48 of the priority valve is acted upon, in the direction of theclosing of the connection between the inlet and the outlet, by apressure prevailing in a first control pressure space 49 connected to aninflow line 13 and, in the direction of the opening of the connection,by a pressure prevailing in a second control pressure space and by aregulating spring 51. When the directional valve 16 is actuated, thesecond control pressure space 50 is connected via the control line 61 toa point downstream of a metering diaphragm 17. The load pressure of thefirst hydraulic consumer 14 then prevails in said second controlpressure space. The regulating spring 51 is formed, for example, in sucha way that there is an equilibrium of forces at the valve member 48 ofthe priority valve 45 when the pressure in the first control pressurespace 49 is 13 bar higher than the pressure in the second controlpressure space 50. This pressure difference is lower than the pressuredifference equivalent to the force of the regulating spring 21 of thepressure compensator 20.

The first hydraulic consumer 14, which is to be supplied as primaryconsumer with pressure medium, is supplied with sufficient pressuremedium, without the priority valve 45 having to come into operation,whenever the sum of the load pressure of said consumer, plus theregulating Δp of the adjustment means 11 on the variable displacementpump 10, is a lower than the highest load pressure of all thesimultaneously actuated second hydraulic consumers 15. This is becausepressure medium always flows to the hydraulic consumer having the lowestload pressure.

The situation will be considered then, where the load pressure of thefirst hydraulic consumer 14 is higher than the highest load pressure ofall the simultaneously actuated second hydraulic consumers 15. It may,for example, be 80 bar, while the highest load pressure of the LUDVconsumers may be 60 bar. When the directional valve 16 is actuated, 80bar then prevail in the control pressure space 50 of the priority valve45. Together with the 13 bar of the regulating spring 51, 93 bar act inthe opening direction of the proportional valve 45. An equilibrium offorces is established at the regulating piston of this valve when 93 barprevail in the first control pressure space 49. Since these 93 bar arehigher than the pressure in the load signaling line 38 by the amount ofthe regulating Δp of the pump regulating valve 39, a pressure of 73 barprevails in the load signaling line 38 in accordance with the regulatingΔ of the variable displacement pump 10 which is in the amount of 20 bar.This pressure also prevails in the control spaces 34 of the pressurecompensators 30. Their metering diaphragms 31 may still be closed.Since, then, the pressure in the system of inflow lines 13 lies abovethe load pressure of the primary hydraulic consumer 14 by the amount ofonly 13 bar, the pressure compensator 20 is fully open and there is apressure drop of only 13 bar across the metering diaphragm 17. If, then,a second hydraulic consumer 15 is to be actuated, the correspondingmetering diaphragm 31 is opened and the corresponding directional valve32 is displaced out of its middle position. Disregarding the influenceof the compression spring 35, the same pressure is established betweenthe metering diaphragm 31 and the following pressure compensator 30 asin the control pressure space 34, specifically a pressure in the amountof 73 bar. For only then does an equilibrium of forces prevail at theregulating piston 33 of the pressure compensator 30. Since the pressureis around 93 bar in the system of inflow lines 13, the pressuredifference across a metering diaphragm 31 amounts, as desired, to 20 barin accordance with the regulating Δp of the variable displacement pump10.

If, then, an increasingly greater pressure medium quantity is demandedfrom the pump as the result of increasing the opening cross section of ametering diaphragm 17 or as the result of increasing the opening crosssections of a plurality of metering diaphragms 31, said pump finallyreaches its point of maximum adjustment, from which there can be nofurther increase in the pressure medium quantity. This leads to areduction in the pressure in the system of inflow lines 13 andconsequently in the first control pressure space 49 of the priorityvalve 45. The regulating piston 48 of the latter is displaced in thedirection of the opening of the connection between the connections 46and 47, so that the pressure in the load signaling line 38 and in thecontrol pressure spaces 34 of the pressure compensators 30 rises. Theregulating pistons 33 of the latter, in turn, reach a state ofequilibrium when the pressure between the metering diaphragms 31 and thepressure compensators 30 is also increased to the value of the pressurein the control pressure spaces 34. The pressure difference across themetering diaphragms 31 is then lower than the regulating Δp of the pump10 in the amount of 20 bar. The pressure medium quantity flowing acrossthe metering diaphragms 31 is reduced correspondingly. Specifically, itis reduced to an extent such that a pressure of 93 bar is maintained inthe system of inflow lines 13. For only then does an equilibrium offorces prevail at the regulating piston 48 of the priority valve. Thus,while the pressure difference across the metering diaphragms 31 isreduced, the pressure difference in the amount of 13 bar is maintainedacross the metering diaphragm 17. In an extreme case, the pressure inthe load signaling line 38 and in the control pressure spaces 34 of thepressure compensators 30 rises to 93 bar, so that pressure medium nolonger flows across the metering diaphragms 31.

In the undersaturation situation described, the pressure compensator 20assigned to the primary hydraulic consumer 14 is fully open. The samepressure therefore prevails at the outlet of the pressure compensator asat the inlet and in the system of inflow lines 13. The first connection46 of the priority valve 45 and the control pressure space 49 cantherefore also be connected, downstream of the pressure compensator, tothe inflow to the directional valve 16. Such a design is shown in FIG.2. The design according to FIG. 2 otherwise corresponds in full to thataccording to FIG. 1, so that reference may be made, in terms of itsmakeup and functioning, to the description of the first exemplaryembodiment.

It may merely be pointed out in addition, with regard to the two designsaccording to FIGS. 1 and 2, that the load signaling line 38 is connectedto the tank 12 via a flow regulator 55. The load signaling line 38 is ineach case relieved of pressure via this flow regulator when none of thehydraulic consumers is actuated.

FIG. 3 shows only the priority valve 45, the pressure compensator 20 andvarious pressure medium routes which lead toward and away from these twovalves and which are located, together with the valves, in a housing 60.The design according to FIG. 3 is largely identical to the designaccording to FIG. 1 and may readily be supplemented by the componentsadditionally shown in FIG. 1. The only difference from the designaccording to FIG. 1 is that, in this case, the control line 61, viawhich the control connection 18 of the directional valve 16 is connectedto the control pressure space 50 of the priority valve 45 and to acontrol pressure space on the pressure compensator 20, is also connectedto the load signaling line 38 via a nonreturn valve 63 located in abypass line 62. At the same time, the nonreturn valve 63 blocks from theload signaling line 38 in the direction of the duct 61, that is to saythe direction of the control connection 18 of the directional valve 16.

Furthermore, a nonreturn valve 64 is also arranged between the secondconnection 47 of the priority valve 45 and the load signaling line 38.Said nonreturn valve blocks in the direction of the connection 47.

In the design according to FIG. 1, the regulating spring 51 of thepriority valve 45 determines the pressure drop at a metering diaphragm17, even when a sufficient quantity of pressure medium is beingconveyed, if the load pressure of the hydraulic consumer 14 to besupplied as primary consumer, minus the difference between the pressureequivalent to the force of the regulating spring 41 of the regulatingvalve 39 and the pressure equivalent to the force of the regulatingspring 51 of the priority valve 45, is greater than the highest loadpressure of all the actuated LUDV consumers 15. This is because apressure is then set in the load signaling line 38, via the priorityvalve 45, which lies below the load pressure of the hydraulic consumer14 to be supplied as primary consumer by the amount of the differencebetween the equivalent pressure of the regulating spring 41 and theequivalent pressure of the regulating spring 51, that is to say, forexample in the case of a load pressure of 80 bar, an equivalent pressureof the regulating spring 41 of 20 bar and an equivalent pressure of theregulating spring 51 in the amount of 13 bar, it is 73 bar. In the eventof undersaturation, the pressure in the load signaling line 38 risesabove this value.

In the design according to FIG. 3, if a sufficient quantity of pressuremedium is conveyed and the primary hydraulic consumer 14 isload-carrying, the load pressure of this hydraulic consumer is guidedvia the nonreturn valve 63 into the load signaling line 38. The pressurein the system of inflow lines 13 is therefore above the load pressure ofthe hydraulic consumer 14 by the amount of the equivalent pressure ofthe regulating spring 41, that is to say by the amount of the regulatingΔp of the variable displacement pump 10, that is to say, in the case ofa load pressure of, for example, 80 bar and a regulating Δp of, forexample, 20 bar, it is 100 bar. Then, as in the case of a load-carryingsecond consumer 15, the pressure drop across a metering diaphragm 17 isdetermined by the force of the regulating spring 21 of the pressurecompensator 20. Only when, in the event of undersaturation, the pressurein the system of inflow lines 13 has fallen to the sum of the loadpressure of the hydraulic consumer 14 plus the pressure equivalent tothe force of the regulating spring 51 of the priority valve 45, that isto say, for example, to 80 bar plus 13 bar equals 93 bar, the pressuredrop across a metering diaphragm 17 of the directional valve 16 is 13bar, that is to say is determined by the force of the regulating spring51. A further reduction in the pressure drop across a metering diaphragm17 does not occur, because, if undersaturation increases further, thepressure in the load signaling line 38 rises via the priority valve 45and the pressure compensators 30 of the LUDV consumers are therebyadjusted in the closing direction.

The nonreturn valve 64 prevents a flow of pressure medium from thehydraulic consumer 14 via the nonreturn valve 63 into the system ofinflow lines 13, insofar as, for example at the commencement ofactuation, the pressure in the inflow lines is not yet above the loadpressure.

What is claimed is:
 1. Hydraulic control circuit for a primary firsthydraulic consumer (14) and for a secondary second hydraulic consumer(15), comprising a first metering device (17), via which pressure mediumcan be supplied to the first hydraulic consumer (14) and via which aconstant pressure difference can be set by means of a preceding pressurecompensator (20), a second metering device (31), via which pressuremedium can be supplied to the second hydraulic consumer (15) and whichis followed by a second pressure compensator (30) which can be actedupon in the closing direction by a control pressure prevailing in a rearcontrol space (34) and in the opening direction by the pressuredownstream of the second metering device (31), a pressure medium source(10) of variable delivery quantity, which is controllable as a functionof the highest load pressure of the actuated hydraulic consumers (14,15) in such a way that the pressure in an inflow line (13) lies abovethe highest load pressure by the amount of a specific pressuredifference, a load signaling line (38) which can be acted upon by theload pressure of the second hydraulic consumer (15) or by a pressurederived therefrom and which is connected to the rear control space (34)of the second pressure compensator (30) and to a regulating member (11)of the pressure medium source (10), and a priority valve (45) which hasa first connection (46), connected to a line section (13) upstream ofthe first metering device (17), and a second connection (47), connectedto the load signaling line (38), and a valve member (48) of which can beacted upon, in the direction of the opening of the connection betweenthe first connection (46) and the second connection (47), by the loadpressure of the primary hydraulic consumer (14) and by an additionalforce (51), wherein the valve member (48) of the priority valve (45) canbe acted upon, in the direction of the closing of the connection betweenthe first connection (46) and the second connection (47), by a pressureprevailing in a line section (13) upstream of the first metering device(17).
 2. Hydraulic control circuit according to claim 1, wherein thevalve member (48) of the priority valve (45) is acted upon in theopening direction by a spring (51).
 3. Hydraulic control circuitaccording to claim 2, wherein the priority valve (45) is formed as aproportional valve.
 4. Hydraulic control circuit according to claim 1,wherein the priority valve (45) is formed as a proportional valve. 5.Hydraulic control circuit according to claim 1, wherein the valve member(48) of the priority valve (45) can be acted upon in the direction ofthe closing by the pressure prevailing in the inflow line (13) upstreamof the first pressure compensator (20).
 6. Hydraulic control circuitaccording to claim 5, wherein a control pressure space (49) on the valvemember (48) of the priority valve (45) and the first connection (46) ofthe priority valve (45) are connected to the inflow to the firstmetering device (17) upstream of the first pressure compensator (20). 7.Hydraulic control circuit according to claim 1, wherein a controlpressure space (49) on the valve member (48) of the priority valve (45)and the first connection (46) of the priority valve (45) are connectedto the inflow to the first metering device (17) on the same side of thefirst pressure compensator (20).
 8. Hydraulic control circuit accordingto claim 1, wherein a flow point is connectable, downstream of the firstmetering device (17), to the load signaling line (38) via a bypass line(62), and that a nonreturn valve (63) opening toward the load signalingline (38) is arranged in the bypass line (62).
 9. Hydraulic controlcircuit according to claim 8, wherein between the nonreturn valve (63)in the bypass line (62) and the second connection (47) of the priorityvalve (45) is arranged a nonreturn valve (64) blocking in the directionof this connection (47).
 10. Hydraulic control circuit according toclaim 1, wherein at least one of said metering devices is a variablerestrictor.